When an infant cannot breathe adequately without assistance, medical personnel may introduce a beveled end of an endotracheal tube into the infant's trachea. One conventional endotracheal tube 10 having a beveled end 12 is illustrated in FIG. 1. An external end 14 of the endotracheal tube 10 is connected to a mechanical ventilator (not shown) which pumps air through the endotracheal tube 10 into the infant's lungs, pauses while the infant exhales, and then repeats this cycle. The ventilator thus introduces oxygen-carrying air into the infant's lungs until such time as the infant is strong enough to breathe on its own. The amount of air pumped during each cycle is calculated according to the infant's lung capacity.
The ventilation system is preferably a "closed system." In a closed system, air pumped into the patient by the ventilator is cleaned to remove hazardous microorganisms. Also, a closed system has no substantial openings in the ventilation circuit through which microorganisms in the ambient environment can easily gain access to the interior of the endotracheal tube 10 and hence to the patient's lungs. In addition to reducing the risk of infection, a closed system is better suited for maintaining PEEP (positive end expiratory pressure) at the internal end 12 of the endotracheal tube 10 to ensure that the air pumped into the ventilation circuit by the ventilator actually reaches the patient's lungs.
To monitor PEEP and other important ventilation characteristics, modern ventilators include various monitoring devices such as the monitor 16 shown in FIG. 1. The monitor 16 is connectable to the endotracheal tube 10 by a conventional ventilation adaptor 18. The ventilation adaptor 18 includes a relatively large-diameter cylindrical extension 20 configured for press-fit connection to a ventilation circuit. The extension 20 is in fluid communication with a smaller-diameter tube 22 that is inserted in the external end 14 of the endotracheal tube 10.
The monitor 16 may be designed to monitor the "tidal volume," that is, the volume of air which moves as the infant inhales and exhales. Changes in tidal volume over time, or tidal volumes which lie outside the expected range, may indicate medical problems in the infant or mechanical problems with the ventilation circuit. The times at which air moves may also be monitored by the monitor 16 in order to synchronize the ventilator's pumping and pausing cycles with the infant's own breathing efforts. Synchronized ventilation has been shown to be more effective in oxygenating the patient's blood and less likely to cause significant damage to the patient's lungs.
In caring for infant patients, it is necessary to periodically suction out secretions which would otherwise accumulate in the infant's lungs. Suctioning is generally accomplished by introducing one end of a flexible suction catheter tube into the endotracheal tube and applying suction to the other end of the catheter tube. To reduce the extent of airway occlusion, the catheter tube is typically withdrawn from the endotracheal tube when the catheter is not in use.
The catheter tube may be an "exposed" catheter tube (not shown) whose only sterility-preserving enclosure is the manufacturer's packaging. An exposed catheter tube cannot be used without removing the tube from its packaging and thereby exposing the tube to an ambient environment which often contains potentially hazardous microorganisms.
In order to reduce the risk of introducing microorganisms into the infant's lungs during use of the suction catheter, many catheters are "sleeved." One conventional sleeved catheter is indicated generally at 30 in FIG. 2. In addition to a catheter tube 32, the sleeved catheter 30 includes a sterile sleeve or sack 34 which substantially encloses the catheter tube 32 to preserve the tube's sterility during use in a closed system. The sleeved catheter 30 also includes a fitting 36 for connecting the catheter 30 to a ventilation circuit.
Although a catheter tube (either sleeved or exposed) may be introduced by temporarily disconnecting a portion of the ventilation circuit to provide access to the endotracheal tube 10, this approach is not preferred. Opening the ventilation circuit interferes with proper ventilation of the infant. In some cases, opening a closed ventilator system leads to brain cell death from anoxia, or to cardiac irregularities such as bradycardia and cardiac arrest. Even if these severe consequences are avoided, opening the ventilation circuit breaches the system's sterility and thus creates a risk of infection in the infant. Introduction of the suction catheter should therefore interfere as little as possible with the continued ventilation of the infant, with the continuous monitoring of that ventilation, and with the sterility of the closed system.
To reduce the adverse impact of suction catheter usage on ventilation, various suction adaptors have been designed. One conventional adaptor, indicated at 40 in FIG. 2, includes three tubes 42, 44, and 46 which meet in a Y-shaped configuration. The bottom leg 42 of the Y-adaptor 40 includes an endotracheal connector which is insertable within the external end 14 of the endotracheal tube 10. One arm 44 of the Y includes a ventilation connector which is connectable to the ventilator by way of additional tubing. The other arm 46 of the Y includes a suction access tube which provides the neonatal suction catheter 30 with access to the endotracheal tube 10. Like the monitor 16 and other devices designed for connection to a ventilation circuit, the Y-adaptor 40 is typically attached to the circuit by press-fit connections which are held in place by friction.
In theory, the Y-adaptor 40 would allow the suction catheter tube 32 access to the endotracheal tube 10 without interrupting ventilation and monitoring, and without opening a sterile closed system. Medical personnel would feed the catheter tube 32 down through the suction access tube 46, into the endotracheal connector 42, and from there into the endotracheal tube 10. The catheter 30 would remain attached to the Y-adaptor 40 and the tube 32 would be withdrawn into its sterile sleeve 34 when not in use, so there would be no need to disconnect the ventilator and the system would remain closed during suction catheter usage.
In practice, however, the endotracheal tube 10 is often inserted in the infant with the ventilation adaptor 18 securely attached to the external end 14 of the endotracheal tube as shown in FIG. 1. Thus, in order to suction the infant's airway it is necessary to remove the endotracheal adaptor 18 from the endotracheal tube 10 and replace it with the Y-adaptor 40 as shown in FIG. 2.
Removing the ventilation adaptor 18 and attaching the Y-adaptor 40 to the endotracheal tube 10 poses numerous risks for the infant. The removal necessarily interrupts ventilation, and thus increases the risk of brain anoxia or cardiac irregularities. The removal also breaches the sterility of the system, thereby increasing the risk of infection. In addition, the twisting, pulling and pushing actions required to replace the ventilation adaptor 18 with the Y-adaptor 40 may cause the endotracheal tube 10 to bruise the infant's breathing passages.
Even if these problems are avoided, maneuvering the catheter tube 32 around the bend 48 between the arm 46 and the leg 42 of the Y-adaptor 40 may cause a kink in the endotracheal tube 10 at or near the edge 50 of the Y-adaptor 40 that interferes with ventilation. Such maneuvering may also cause a kink in the catheter tube 32 that interferes with suctioning.
Accordingly, some conventional suction adaptors are "straight" adaptors which allow the catheter tube to travel in a substantially straight line in or out of the endotracheal tube. A straight adaptor includes a suction access tube that provides endotracheal tube access to a suction catheter. The straight adaptor also includes a tubular endotracheal connector that is connectable to the ventilation adaptor of an endotracheal tube, and a tubular ventilation connector that is connectable to a ventilator. The suction access tube and the endotracheal connector are substantially aligned in that their central longitudinal axes are collinear.
Thus, the straight adaptor is essentially a Y-adaptor in which the leg and one arm of the Y have been moved into alignment, and which connects to the endotracheal tube ventilation adaptor rather than connecting directly to the endotracheal tube. The straight adaptor avoids the problems created by the bend between a Y-adaptor's arm and leg by simply removing the bend. The straight adaptor avoids the problems created by removal of the endotracheal tube ventilation adaptor by connecting to that adaptor rather than removing and replacing it.
However, straight adaptors, Y-adaptors, and other conventional suction adaptors all derive their internal configurations from suction adaptors that are intended for use in treating adult patients rather than neonates. As a consequence, conventional neonatal suction adaptors have a relatively large effective internal volume, which in turn increases the effective internal volume of the entire ventilation circuit. The effective internal volume of an adaptor or a ventilation circuit is also known as the "deadspace" of the adaptor or the circuit, respectively.
The deadspace includes spaces inside the ventilation circuit which are in fluid communication with the infant's lungs. If the amount of deadspace is too great, the infant's exhalations will not be substantially cleared from the ventilation circuit but will rather remain behind in the deadspace. This previously breathed air will then be re-inhaled on the infant's next breath. If the infant rebreathes too great a portion of its exhalations, the infant will retain carbon dioxide rather than receiving oxygen. Brain anoxia, cardiac irregularities, and death may follow.
Likewise, if the ventilation circuit contains excessive deadspace, the ventilator will ventilate the deadspace rather than ventilating the infant's lungs. Oxygenated air will be pumped into the ventilation circuit by the ventilator during "inhalation," but rather than being inhaled by the infant, the oxygenated air will remain within the deadspace. On exhalation, the oxygenated air will be expelled from the circuit without ever having reached the infant.
Adequate ventilation of an infant is generally difficult or impossible if the amount of deadspace inside the ventilation circuit exceeds about one-third of the infant's tidal volume. The tidal volume of a neonatal patient is typically in the range from about three to about six cubic centimeters per pound of body weight. For instance, an infant weighing about 1000 grams (about two pounds) normally has a tidal volume in the range from about six to about 12 cubic centimeters.
Because neonatal patients have significantly smaller tidal volumes than other patients, they are significantly more sensitive than other patients to small changes in the volume of deadspace within an adaptor. A change of one or two cubic centimeters in the deadspace of an infant's ventilation circuit may mean the difference between life and death. For instance, a ventilation circuit having five cubic centimeters of deadspace could be fatal to a two-pound infant which is effectively ventilated once the circuit's deadspace is reduced to three cubic centimeters.
The need to reduce deadspace is not even recognized in conventional neonatal suction adaptors, much less adequately addressed. The ventilator connectors, endotracheal tube connectors, and suction access tubes of conventional neonatal adaptors are configured merely with a view toward providing press-fit connections to standard size ventilator tubes, endotracheal tubes, sleeved catheters, and other devices. Thus, the internal dimensions of these elements of conventional adaptors often contribute excessive deadspace to the ventilation circuit. Likewise, many conventional straight adaptors include additional tubes or connectors which allow temperature sensors, pressure sensors, and other devices to be connected to the adaptor. These additional tubes increase the deadspace of the ventilation circuit by providing volumes which may trap oxygenated air intended for the infant or volumes which may trap the infant's exhalations and permit excessive rebreathing of those exhalations.
Thus, it would be an advancement in the art to provide a neonatal suction adaptor which has less deadspace than conventional adaptors.
It would also be an advancement in the art to provide such a neonatal suction adaptor which allows a catheter tube to travel substantially unobstructed in and out of the endotracheal tube.
It would be a further advancement to provide such a neonatal suction adaptor which is easily connected with a wide variety of conventional sleeved catheters, ventilation monitors, and endotracheal tubes to form a closed system.
It would be an additional advantage to provide such a neonatal suction adaptor which allows the use of a suction catheter without substantial interruption of neonatal tidal volume monitoring and synchronization.
Such a neonatal suction adaptor is disclosed and claimed herein.